bpdc is "back post double crochet" and fpdc is "front post double crochet"Essentialy you double crochet as normal but instead of going into the top of the stitch you crochet around the post of the stitch. If you go around the post from the front it is a fpdc and if you go around from the back it is a bpdc. There are many you tube videos where you can see someone actually doing the stitch. If you would like to see a video sowing the technique and can't find any let me know and I will help you find a good onePatty